Torque fluctuation absorbing device

ABSTRACT

A torque fluctuation absorbing device includes a first rotational member transmitted with a torque from a driving power source, a damping mechanism connected with an input shaft of a transmission, the damping mechanism having a pair of frictional members of approximately annular-shaped fixed at both surfaces of a disc, and a limiter portion for frictionally engaging the pair of frictional members with the first rotational member in a substantially direct manner or in a substantially indirect manner via a pair of frictional plates. An actual length of at least one of the pair of frictional members ranges substantially between 1 percent and 6 percents of a major diameter of the at least one of the pair of frictional members.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. § 119with respect to Japanese Patent Application 2003-337132, filed on Sep.29, 2003, the entire content of which is incorporated herein byreference.

FIELD OF THE INVENTION

This invention generally relates to a torque fluctuation absorbingdevice which is disposed between a driving power source and atransmission and is able to absorb torque fluctuation caused between thedriving power source and the transmission. More particularly, thisinvention pertains to a torque fluctuation absorbing device capable ofreducing fluctuation of a limit torque value.

BACKGROUND

There have been torque fluctuation absorbing devices widely known, whichare able to absorb torque fluctuation generated between a driving powersource (e.g., an internal combustion engine and an electric motor) and atransmission. A conventional torque fluctuation absorbing device isprovided with a damping mechanism, which is capable of absorbingfluctuation of a torque transmitted to a flywheel from the driving powersource, and a limiter portion, which is capable of limiting a torque tobe transmitted from the flywheel to a transmission input shaft when afluctuating torque between the damping mechanism and the flywheelreaches a predetermined value, i.e., a limit torque value. The flywheelis connected to the driving power source, such as a crankshaft of theinternal combustion engine.

The damping mechanism is connected to the transmission input shaft. Thedamping mechanism includes frictional members that are respectivelyattached at both surfaces at an outer circumferential portion of adamper disc. At the limiter portion, the frictional members of thedamping mechanism is frictionally engaged with the flywheel in a directmanner or in an indirect manner via a frictional plate. The limit torquevalue, at which the frictional members at the limiter portion startsslipping, varies across the ages in response to the number of theoperations of the limiter portion. Therefore, when the limit torquevalue widely increases, an excessive torque may be inputted to thetransmission. On the other hand, when the limit torque value widelydecreases, the frictional members may be transmitted with a torquesmaller than a normal torque. In this case, a sufficient torque may notbe transmitted to the transmission such that a vehicle acceleratingperformance may be deteriorated. Frictional powder of the frictionalmembers seems to be one of the factors causing the above.

In light of foregoing, JP2003-194095A2 discloses a torque fluctuationabsorbing device having frictional members at a limiter portion, both ofwhich have penetrating slits in order to emit the frictional powder ofthe frictional members into an external ambient environment by acentrifugal force. Accordingly, the limit torque value can beeffectively stabilized.

However, in the above-described torque fluctuation absorbing device, africtional surface of each frictional member at the limiter portion canmore stably and frictionally engaged with the flywheel so as tostabilize the limit torque value more reliably.

A need exists for providing an improved torque fluctuation absorbingdevice capable of reducing a fluctuation of a limit torque value,especially an age-based change of a limit torque value.

SUMMARY OF THE INVENTION

According to an aspect of a present invention, a torque fluctuationabsorbing device includes a first rotational member transmitted with atorque from a driving power source, a damping mechanism connected withan input shaft of a transmission, the damping mechanism having a pair offrictional members of approximately annular-shaped fixed at bothsurfaces of a disc, and a limiter portion for frictionally engaging thepair of frictional members with the first rotational member in asubstantially direct manner or in a substantially indirect manner via apair of frictional plates. An actual length of at least one of the pairof frictional members ranges substantially between 1 percent and 6percents of a major diameter of the at least one of the pair offrictional members.

According to another aspect of the present invention, a torquefluctuation absorbing device includes a first rotational membertransmitted with a torque from a driving power source, a dampingmechanism connected with an input shaft of a transmission, the dampingmechanism having a pair of frictional members of approximatelyannular-shaped fixed at both surfaces of a disc, and a limiter portionfor frictionally engaging the pair of frictional members with the firstrotational member in a substantially direct manner or in a substantiallyindirect manner via a pair of frictional plates. At least one of thepair of frictional members includes a non-frictional portion at a ratesubstantially between 20 percents and 80 percents of an entirefrictional surface area of the at least one of the pair of frictionalmembers.

According to further aspect of the present invention, a torquefluctuation absorbing device includes a first rotational membertransmitted with a torque from a driving power source, a dampingmechanism connected with an input shaft of a transmission; the dampingmechanism having a pair of frictional members of approximatelyannular-shaped fixed at both surfaces of a disc, and a limiter portionfor frictionally engaging the pair of frictional members with the firstrotational member in a substantially direct manner or in a substantiallyindirect manner via a pair of frictional plates. At least one of thefrictional members is configured with plural frictional materials ofapproximately block-shaped, the at least one of the frictional membersis allocated at the disc so as to range a frictional surface of the atleast one of the frictional members substantially between 20 percentsand 80 percents of an entire surface area of the disc at which the atleast one of the frictional members can be allocated.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and additional features and characteristics of the presentinvention will become more apparent from the following detaileddescription considered with reference to the accompanying drawings,wherein:

FIG. 1 is a part cutaway view illustrating a torque fluctuationabsorbing device according to a first embodiment of the presentinvention;

FIG. 2 is a sectional view of the torque fluctuation absorbing devicetaken along a line A–A′ in FIG. 1;

FIG. 3A is a part plan view schematically illustrating a disc and africtional member at a limiter portion of the torque fluctuationabsorbing device according to the first embodiment of the presentinvention;

FIG. 3B is a part sectional view illustrating the disc and thefrictional member at the limiter portion in FIG. 3A on a large scale;

FIG. 4A is a part plan view schematically illustrating the disc and thefrictional member at the limiter portion of the torque fluctuationabsorbing device according to a second embodiment of the presentinvention;

FIG. 4B is a part sectional view illustrating the disc and thefrictional member at the limiter portion in FIG. 4A on a large scale;

FIG. 5A is another part plan view schematically illustrating the discand the frictional member at the limiter portion of the torquefluctuation absorbing device according to the second embodiment of thepresent invention;

FIG. 5B is another part sectional view illustrating the disc and thefrictional member at the limiter portion in FIG. 5A on a large scale;

FIG. 6A is a part plan view schematically illustrating the disc and thefrictional member at the limiter portion of the torque fluctuationabsorbing device according to a third embodiment of the presentinvention;

FIG. 6B is a part sectional view illustrating the disc and thefrictional member at the limiter portion in FIG. 6A on a large scale;

FIG. 7A is a part plan view schematically illustrating the disc and thefrictional member at the limiter portion of the torque fluctuationabsorbing device according to a fourth embodiment of the presentinvention;

FIG. 7B is a part sectional view illustrating the disc and thefrictional member at the limiter portion in FIG. 7B on a large scale;

FIG. 8 is a diagram for explaining a durability test result of thetorque fluctuation absorbing device according to the first embodiment ofthe present invention;

FIG. 9 is a diagram for explaining an age-based change of a limit torquevalue (corresponding to B/D (%) in FIG. 2) of the frictional member withrespect to each actual length;

FIG. 10 is a diagram for explaining a durability test result of a torquefluctuation absorbing device according to the second embodiment of thepresent invention; and

FIG. 11 is a diagram for explaining an age-based change of a limittorque value of the frictional member with respect to each area of thegroove.

DETAILED DESCRIPTION

Embodiments of the present invention will be described hereinbelow indetail with reference to the accompanying drawings.

As illustrated in FIGS. 1, 2, 3A and 3B, a torque fluctuation-absorbingdevice 1 includes a support plate 10, a damping mechanism 20 and alimiter portion 30. The support plate 10 is a first rotational memberconfigured to transmit a driving torque from a driving power source suchas an engine to the damping mechanism 20. The damping mechanism 20 isadjusted to absorb fluctuation of a driving torque at the support plate10 connected to a crankshaft of the engine. When the fluctuating torquebetween the damping mechanism 20 and the support plate 10 reaches apredetermined value, i.e., a limit torque value, the limiter portion 30limits the torque to be transmitted from the support plate 10 to atransmission input shaft.

The damping mechanism 20 includes a hub 21, a side plate 22, a thrustmember 23, a damper 24, a disc 25, a pair of frictional members 26 and arivet. The hub 21 is integrally provided with a flange portion 21 aextending radially outwardly. The hub 21 is further provided with aspline portion 21 b at an inner surface of a central bore thereof, whichis spline engaged with the transmission input shaft. There are at leastone notched portion 21 c defined at a radially outer side of the flangeportion 21 a. According to the first embodiment of the presentinvention, there are four notched portions 21 c defined at a radiallyouter side of the flange portion 21 a. A pair of spring seats 24 a isdisposed in each notched portion 21 c, and an outer peripheral surfaceof the spring seat 24 a is positioned to be outside of a radially outerside of an outer peripheral surface of the flange portion 21 a.

The side plate 22 includes a first side plate 22A and a second sideplate 22B. As illustrated in FIG. 2, the first and second side plates22A and 22B are oriented along both axial surfaces of the flange portion21 a to be substantially coaxial with the hub 21, respectively. Thefirst and second side plates 22A and 22B rotate relative to the hub 21.Each of the first and second side plates 22A and 22B has a penetratinghole at a radially outer portion thereof so as to be riveted with thedisc 25 together. Each of the first and second side plates 22A and 22Bhas at least one window bore 22 c for housing the damper 24 therein.According to the first embodiment of the present invention, there arefour window bores 22 c for housing the dampers 24 therein, respectively.

The thrust member 23 is an approximately ring-shaped member disposedbetween an inner surface of the side plate 22 and an outer surface ofthe hub 21. The inner surface of the side plate 22 becomes in contactwith the outer surface of the hub 21. The thrust member 23 includes afirst thrust member 23A, which is disposed between the outer surface ofthe hub 21 and the inner surface of the first side plate 22A, a secondthrust member 23B, which is disposed between the outer surface of thehub 21 and the inner surface of the second side plate 22B, and a discspring 23 c (i.e., biasing means). Therefore, a hysteresis torque isgenerated between the flange portion 21 a of the hub 21 and the sideplate 22. The disc spring 23 c is not limited to a disc spring.

The damper 24 includes a coil spring and is housed in the notchedportion 21 c of the hub 21 and the window bore 22 c of the side plate22. The notched portions 21 c substantially face the window bores 22 c,respectively.

The disc 25 is an approximately annular-shaped disc and extends in amore radially outward direction than an outer circumference of the sideplate 22. A vicinity of an inner circumference of the disc 25 has beenheld by the side plate 22 and includes a penetrating hole for connectingthe disc 25 with the side plate 22. The pair of frictional members 26 ofapproximately annular-shaped is fixed at both axial surfaces of the disc25, as illustrated in FIG. 2. According to the first embodiment of thepresent invention, the pair of frictional members 26 is adhered at theboth surfaces of the disc 25 with an adhesive. A frictional surface ofthe one frictional member 26 (illustrated at a right side in FIG. 2) isheld by a first frictional surface plate 31, while a frictional surfaceof the other frictional member 26 (illustrated at a left side in FIG. 2)is held by a second frictional surface plate 32. In order to improve acontact performance of a frictional surface of the frictional members26, an actual length of at least one of the frictional members 26 in aradial direction thereof ranges substantially between 1% and 6%inclusive, of a major diameter of the frictional member 26. The actuallength of the frictional member 26 is indicated with an alphabetic markB in FIG. 2. Therefore, the rate of the actual length of the frictionalmember 26 relative to the major diameter of the frictional member 26 canbe denoted with B/D (%). It is preferable that the rate rangessubstantially between 2% and 6%, inclusive. It is further preferablethat the rate ranges substantially between 3% and 6%, inclusive.

At least one of the frictional members 26 (both of them according to thefirst embodiment) has at least one projected portion 26 d in order toimprove a fixing performance between the frictional member 26 and thedisc 25, as illustrated in FIG. 3B. It is preferable that the disc 25has a recessed portion such as a concave portion, a bore and so on, inwhich the projected portion 26 d fits. This structure of the frictionalmember 26 and the disc 25 can be applied to second, third and fourthembodiments (described later). Further, the frictional member 26 canhave a groove (not shown) for emitting frictional powder generated inresponse to the frictional engagement. The frictional powder of thefrictional member 26 can be emitted into an outer ambient environment byuse of a centrifugal force. The groove can be a slit communicatingbetween a radially inner side of the frictional member 26 and a radiallyouter side thereof. Still further, it is preferable that the frictionalmember 26 is made of a material having an elastic force so as tosubstantially uniformly and frictionally engage the frictional surfaceof each frictional member 26 with the frictional surface plate.

The rivet 27 connects the disc 25 with the side plate 22.

The limiter portion 30 includes the first frictional surface plate 31,the second frictional surface plate 32, a disc spring 33 and a rivet 34.The limiter portion 30 can be interpreted to also include the frictionalmembers 26. As illustrated in FIG. 2, the first frictional surface plate31 is fixed at the support plate 10 via the rivet 34. The firstfrictional surface plate 31 is frictionally engaged with the onefrictional member 26 (illustrated at the right side in FIG. 2) from aside opposite to the support plate 10. The first frictional surfaceplate 31 can have a hole or groove (not shown) in order to emit africtional powder of the frictional members 26 into an outer ambientenvironment. The second frictional surface plate 32 is frictionallyengaged with the other frictional member 26 (illustrated at the leftside in FIG. 2) from a side of the support plate 10. The disc spring 33is oriented between the support plate 10 and the second frictionalsurface plate 32 and biases the second frictional surface plate 32 in aright direction in FIG. 2, i.e., in a direction for keeping the secondfrictional surface plate 32 away from the support plate 10. Therefore,The frictional members 26 can be held by the first frictional surfaceplate 31 and the second frictional surface plate 32 such that thesupport plate 10 and the damping mechanism 20 can be maintained at africtionally engaged condition. The rivet 34 fixes the support plate 10and the first frictional surface plate 31.

As described above, according to the first embodiment of the presentinvention, the frictional members 26 are held by the first frictionalsurface plate 31 and the second frictional surface plate 32.Alternatively, a frictional member can be disposed between a portion ofthe support plate 10 and the second frictional surface plate 32. In thiscase, when the fluctuating torque reaches the predetermined value (i.e.,limit torque value), the frictional member slips relative to the supportplate 10.

Next, following explanation will be given for explaining an operation ofthe torque fluctuation-absorbing device 1 with the above-describedstructure.

When the engine is driven, the support plate 10 rotates in response tothe driving force from the engine. While the fluctuating torque issmaller than the limit torque value, a rotational torque is transmittedto the disc 25 of the damping mechanism 20 and the side plate 22 via thelimiter portion 30, wherein the damping mechanism 20 rotates. Therotational torque of the side plate 22 is transmitted to the hub 21 viathe damper 24, the thrust member 23 and the flange portion 21 a, whereinthe hub 21 starts rotating. In this case, the damper 24 is elasticallycompressed in response to the amount of the fluctuating torque. Asdescribed above, the driving force of the diving power source istransmitted to the transmission input shaft via the damping mechanism20.

In the torque fluctuation absorbing device 1 functioning as describedabove, when the floating torque between the support plate 10 and the hub21 reaches the limit torque value in response to increase of the drivingtorque from the engine, the frictional members starts slipping.Therefore, a torque over the limit torque value can be prevented frombeing transmitted between the side plate 22 and the hub 21. A timing, atwhich the torque between the support plate 10 and the hub 21 reaches thelimit torque value, substantially corresponds to a timing at which thetorque reaches a holding torque for holding the frictional members 26between the first frictional surface plate 31 and the second frictionalsurface plate 32 in a rotational direction of the frictional members 26.

Next, following explanation will be given for explaining some of theeffects according to the first embodiment of the present invention withthe attached drawings.

As testing conditions of the durability test of the torque fluctuationabsorbing device 1 illustrated in FIG. 1, the torque fluctuation isinputted into the torque fluctuation absorbing device 1 at thepredetermined number of times by repeatedly starting and stopping theengine activation. The y-axis of the diagram in FIG. 8 indicates a rateof an increase of the limit torque value under a condition that aninitial limit torque value at the first use of this device issubstantially zero percent. The x-axis thereof indicates a time transitfor transmitting the torque fluctuation to this device 1 at thepredetermined number of times. The predetermined number of times fortransmitting the torque fluctuation to this device 1 can be determinedbased upon the number of torque fluctuations detected while a vehicleactually has run about 100,000 kilometers. Broken lines in FIG. 8 showthe age-based changes of the limit torque values of the frictionalmember 26, of which actual lengths (corresponding to B/D (%) in FIG. 2)are set at 15 percents and 30 percents of the major diameter of thefrictional member 26, respectively. According to the results explainedby these two broken lines in FIG. 8, there is an immediate sharpincrease in the limit torque value of each frictional member 26immediately after the test starting. As time goes, each limit torquevalue becomes steady at an approximately 50 percents increase relativeto the limit torque value at the substantially zero percent. This testresult shows that an upper threshold torque to be transmitted to thetransmission increases at 1½ times of the initial limit torque.Accordingly, the transmission is inputted excessive torque fluctuationsuch that the transmission may be subjected with a load.

On the other hand, two solid lines in FIG. 8 show the age-based changesof the limit torque values of the frictional member 26, of which actuallengths (corresponding to B/D (%) in FIG. 2) are set at 1 percent and 6percents of the major diameter of the frictional member 26,respectively. According to the results explained by these two solidlines in FIG. 8, each limit torque value becomes steady at anapproximately 30-percent increase relative to the limit torque value atthe substantially zero percent. This test results shows that theage-based change (i.e., increasing rate) of the limit torque value ofthe frictional member 26 can be effectively restrained.

FIG. 9 is a diagram for explaining an age-based change of the limittorque value (corresponding to B/D (%) in FIG. 2) of the frictionalmember 26 with respect each actual length. FIG. 9 shows a stabledincreasing rate of the frictional member 26 having each actual lengthindicated by the x-axis in the diagram. As illustrated in FIG. 8, thestabled increasing rate is detected by inputting the torque fluctuationat the predetermined number of times. As explained in FIG. 9, the limittorque value is increased at a rate of less than 30 percents relative tothe initial limit torque value when the actual length of the frictionalmember 26 ranged between 1 percent and 6 percents, inclusive. However,once the actual length of the frictional member 26 exceeds 10 percentsof the major diameter of the frictional member 26, the limit torquevalue is increased more than 50 percents of the initial limit torquevalue.

As described above, according to the first embodiment of the presentinvention, it is preferable that the radial actual length of thefrictional member 26 ranges substantially between 1 percent and 6percents of the major diameter of the frictional member 26, in order toimprove a contact performance of the frictional members 26.

Next, the following explanation will be given for explaining a secondembodiment of the present invention with reference to FIGS. 4A, 4B, 5Aand 5B.

In the torque fluctuation absorbing device 1 according to the secondembodiment of the present invention, there is a difference in astructure of the frictional members 26 fixed at the disc 25 from the oneaccording to the first embodiment of the present invention. The othercomponents of the torque fluctuation absorbing device 1 according to thesecond embodiment of the present invention possess the same constructionas the ones according to the first embodiment and so a detaileddescription thereof will be omitted hereinbelow.

In order to improve the contact performance of each frictional member26, at least one of the frictional members 26 has a non-frictionalportion (i.e., groove 26 a) ranging substantially between 20 percentsand 80 percents of an entire frictional surface area of the at least oneof the frictional members 26. It is preferable that the frictionalmember 26 is designed to have the non-frictional portion rangessubstantially between 30 percents and 70 percents of the entirefrictional surface area of the frictional member 26. It is morepreferable that the non-frictional portion ranges substantially between40 percents and 60 percents thereof. The non-frictional portion can be arecessed portion such as a concave portion, a groove and so on asnon-limiting examples. Further, it is preferable that the non-frictionalportion such as the groove 26 a communicates between the innerperipheral side of the frictional member 26 and the outer peripheralthereof so as to emit the frictional powder of the frictional members 26into the outer ambient environment by use of the centrifugal force.According to the second embodiment of the present invention, the pair offrictional members 26 is adhered at the both surfaces of the disc 25with the adhesive. In order to increase the adhesive force between thedisc 25 and the frictional members 26, the disc 25 can preferably havean axially penetrating hole. The pair of frictional members 26 isprovided with a bridging portion 26 e for integrally connecting thefrictional members 26 through the penetrating hole. This structure canbe applied to the first, third and fourth embodiments. It is preferablethat the fictional members 26 are made of a material having an elasticforce so as to substantially uniformly and frictionally engage thefrictional surface of each frictional members 26 with the frictionalsurface plate.

Next, following explanation will be given for explaining some of theeffects according to a second embodiment of the present invention withthe attached drawings.

As testing conditions of the durability test of the torque fluctuationabsorbing device 1 illustrated in 1, the torque fluctuation is inputtedinto the torque fluctuation absorbing device 1 at the predeterminednumber of times by repeatedly starting and stopping the engineactivation. The y-axis of the diagram in FIG. 10 indicates a rate of anincrease of the limit torque value under a condition that an initiallimit torque value at the first use of this device is substantially zeropercent. The x-axis thereof indicates a time transit for transmittingthe torque fluctuation to this device 1 at the predetermined number oftimes. The predetermined number of times for transmitting the torquefluctuation to this device 1 can be determined based upon the number oftorque fluctuations detected while a vehicle actually has run about100,000 kilometers. Broken lines in FIG. 10 show the age-based changesof the limit torque values of the frictional member 26 of which groove26 a is set at 15 percents and 90 percents of the entire frictionalsurface area of the frictional member 26, respectively. According to theresults explained by these two broken lines in FIG. 10, there is animmediate sharp increase in the limit torque value of the frictionalmember 26, of which groove 26 a is set at 15 percents. As time goes, theincreasing rate of the limit torque value of the frictional member 26remains around 60 percents. Meanwhile, there is a 30-percent increase inthe limit torque value of the frictional member 26, of which groove 26 ais set at 90 percents, as time goes. (P shown in FIG. 10) The changerate of the limit torque value then falls right down. (Q shown in FIG.10) This rapid drop implies a rapid wear-out of the frictional member 26due to few frictional area of the frictional member 26 under a conditionthat the groove 26 a is set at 90 percents of the entire frictionalsurface area of the frictional member 26.

On the other hand, two solid lines in FIG. 10 show the age-based changesof the limit torque values of the frictional member 26 of which groove26 a is set at 20 percents and 80 percents of the entire frictionalsurface area of the frictional member 26, respectively. According to theresults explained by these two solid lines in FIG. 10, each limit torquevalue becomes steady at an approximately 30-percent increase relative tothe limit torque value at the substantially zero percent. This testresults show that the age-based change (i.e., increasing rate) of thelimit torque value of the frictional member 26 can be effectivelyrestrained.

FIG. 11 is a diagram for explaining an age-based change of the limittorque value of the frictional member 26 with respect each rate of thegroove area. FIG. 11 shows a stabled increasing rate of the frictionalmember 26 having each actual groove area rate (amount) indicated by thex-axis in the diagram. As illustrated in FIG. 10, the stabled increasingrate is detected by inputting the torque fluctuation at thepredetermined number of times. As explained in FIG. 11, when the area ofthe groove 26 a ranges substantially between 20 percents and 80 percentsof an entire frictional surface area of each frictional member 26, thechange rate of the limit torque value is effectively restrained at anapproximately 30 percents. This test results show that the limit torquevalue can be stabilized because the frictional powder of the frictionalmember 26 can be effectively emitted through the groove 26 a. Therefore,the limit torque value can be effectively stabilized. Also, P,Q in FIG.11 are corresponding to P,Q in FIG. 10 especially the value of Q showsthe value of difference between the maximum and minimum of the limittorque value of the frictional member 26, of which groove 26 a is set at90 percents.

Next, the following explanation will be given for explaining a thirdembodiment of the present invention with reference to FIGS. 6A and 6B.

In the torque fluctuation absorbing device 1 according to the thirdembodiment of the present invention, there is a difference in astructure of the frictional member 26 fixed at the disc 25 from the oneaccording to the first embodiment of the present invention. The othercomponents of the torque fluctuation absorbing device 1 according to thethird embodiment of the present invention possess the same constructionas the ones according to the first embodiment of and so a detaileddescription thereof will be omitted hereinbelow.

In order to improve the contact performance of each frictional member26, at least one of the frictional members 26 is configured with pluralblock-shaped frictional materials. The frictional member 26 is allocatedat the disc 25 so as to set a frictional surface of the frictionalmember 26 substantially between 20 percents and 80 percents of an entiresurface area of the disc 25, at which the frictional member 26 can beallocated. It is preferable that the area of the plural block-shapedmaterials ranges substantially between 30 percents and 70 percents ofthe entire surface area of the disc 25. It is more preferable that thearea of the plural block-shaped materials ranges substantially between40 percents and 60 percents of the entire surface area thereof. There isa blank portion 26 c between the adjacent block-shaped materials of eachfrictional member 26. Hereinafter, an area, at which the frictionalmember 26 can be allocated at the disc 25, substantially corresponds toan area excluding an area, which can come in contact with the side plate22, when the disc 25 is riveted with the side plate 22.

An area, at which the frictional member 26 has not been allocated in thearea at which the frictional member 26 can be allocated, can preferablycommunicate between the inner peripheral side and the outer peripheralside in order to emit the frictional powder of the frictional members 26into the external ambient environment by use of the centrifugal force.Although not being illustrated, in order to improve the contactperformance of the block-shaped materials 26, it is preferable that anon-frictional portion is defined at the frictional surface thereof. Thenon-frictional portion can be substantially the same as the groove 26 ain FIG. 4. The non-frictional portion can be a recessed portion such asa groove, a concave portion and so on as non-limiting examples. Further,it is preferable that the non-frictional portion such as the groovecommunicates between the inner peripheral side and the outer peripheralside of the frictional member 26 so as to emit the frictional powder ofthe frictional members 26 into the outer ambient environment by use ofthe centrifugal force. According to the third embodiment of the presentinvention, the pair of frictional members 26 is adhered at the bothsurfaces of the disc 25 with the adhesive. In order to increase theadhesive force between the disc 25 and the frictional members 25, atleast one of the frictional members 26 has at least one projectedportion in the same manner as the projected portion 26 d illustrated inFIG. 3. It is preferable that the disc 25 has a recessed portion such asa concave portion or a bore, in which the projected portion fits. It isfurther preferable that the pair of frictional members 26 is providedwith a bridging portion (similar to the bridging portion 26 e in FIG. 4)for integrally connecting the frictional members 26 through apenetrating hole at the disc 25. It is still further preferable that thefrictional member 26 is made of a material having an elastic force so asto substantially equalize a contact performance of the frictionalsurface of each frictional member 26.

Some of the effects according to the third embodiment of the presentinvention is substantially the same as the effects according to thesecond embodiment.

Next, the following explanation will be given for explaining a fourthembodiment of the present invention with reference to FIGS. 7A and 7B.

The torque fluctuation absorbing device 1 according to the fourthembodiment of the present invention is provided with a reinforcingmember 26 b. The reinforcing member 26 b can be integral with at leastone of the frictional members 26 according to the first, second andthird embodiments of the present invention. The reinforcing member 26 bpossesses a stronger property than the frictional members 26. The othercomponents of the torque fluctuation absorbing device 1 according to thefourth embodiment of the present invention possesses the sameconstruction as the ones according to the first, second and thirdembodiments and so a detailed description thereof will be omittedhereinbelow. On the basis of the cross sectional view of the frictionalmember 26 as illustrated in FIG. 7B, the reinforcing member 26 bprojects at both radial ends portions of the frictional surface lessthan at the vicinity of a central portion of the frictional surface. Inthe frictional member 26 according to the second and third embodimentsof the present invention, it is preferable that the reinforcing members26 b projects at both radial ends portions of the frictional surfaceless than at the vicinity of the central portion thereof. Thereinforcing member 26 b can be made of a heat-resisting fiber such as aglass fiber, a carbon fiber, a metal fiber, an asbestos, an alamidofiber and so on as non-limiting examples. Therefore, the frictionalplates can be effectively prevented from being damaged by an edge of thereinforcing member 26 b. A surface roughness of the correspondingfrictional surface can be restrained from being changed such that thelimit torque value can be stabilized.

Next, following explanation will be given for explaining a fifthembodiment of the present invention with reference to the attacheddrawings. The torque fluctuation absorbing device 1 according to thefifth embodiment of the present invention is different from the devicesaccording to the first, second, third and fourth embodiments, in which africtional surface of at least one of the frictional surface plates 31and 32 and the frictional surface of at least one of the frictionalmembers 26 corresponding to the at least one of the frictional surfaceplates 31 and 32 are roughened, for example shot peening, bonderizingprocess and so on. Apart from the roughened frictional surface thereof,the device 1 according to the fifth embodiment of the present inventionis substantially the same as the device 1 according to the first,second, third and fourth embodiments.

As described above, according to the fifth embodiment of the presentinvention, the corresponding frictional surfaces of the at least one ofthe frictional surface plate and the frictional member can be roughened,thereby enabling to increase only an initial frictional coefficient.Therefore, if the only initial frictional coefficient, which has acharacteristic of age-based increase, is increased, the change rate ofthe frictional coefficient is decreased such that the limit torque valuecan be effectively stabilized.

The principles, embodiments and modes of operation of the presentinvention have been described in the foregoing specification anddrawings. However, the invention which is intended to be protected isnot to be construed as limited to the particular embodiments disclosed.Further, the embodiments described herein are to be regarded asillustrative rather than restrictive. Plural objectives are achieved bythe present invention, and yet there is usefulness in the presentinvention as far as one of the objectives are achieved. Variations andchanges may be made by others, and equivalents employed, withoutdeparting from the spirit of the present invention. Accordingly, it isexpressly intended that all such variations, changes and equivalentswhich fall within the spirit and scope of the present invention asdefined in the claims, be embraced thereby.

1. A torque fluctuation absorbing device comprising: a first rotationalmember which transmits a torque from a driving power source; a dampingmechanism connected with an input shaft of a transmission, the dampingmechanism comprising coil springs positioned between a side plate and ahub; and a limiter portion comprising a pair of approximatelyannular-shaped frictional members fixed at both surfaces of a discconnected with the side plate, the pair of frictional members constantlyengaging the first rotational member in a direct manner or in anindirect manner via a pair of frictional plates by a disc spring;wherein the pair of frictional members are positioned at an outer sideof the coil springs in a radial direction, and at least one of the pairof frictional members includes a non-frictional portion at a ratesubstantially between 20 percent and 80 percent of an entire frictionalsurface area of the at least one of the pair of frictional members.
 2. Atorque fluctuation absorbing device according to claim 1, wherein the atleast one of the pair of frictional members is adhered at the disc.
 3. Atorque fluctuation absorbing device according to claim 1, wherein the atleast one of the pair of frictional members includes a projectedportion, and the disc includes a recessed portion for fitting theprojected portion therein.
 4. A torque fluctuation absorbing deviceaccording to claim 1, wherein the disc includes a hole for integrallyconnecting one of the pair of frictional members fixed at a firstsurface of the disc with the other one of the pair of frictional membersfixed at a second surface of the disc.
 5. A torque fluctuation absorbingdevice according to claim 1, wherein at least one of the pair offrictional members includes a reinforcing member which is more rigidthan the at least one of the pair of frictional members, and thereinforcing member projects at both radial end portions of thefrictional surface less than at the vicinity of a central portion of thefrictional surface on the basis of a cross sectional view of thefrictional member.
 6. A torque fluctuation absorbing device comprising:a first rotational member which transmits a torque from a driving powersource; a damping mechanism connected with an input shaft of atransmission; the damping mechanism having a pair of frictional membersof approximately annular-shape fixed at both surfaces of a disc; and alimiter portion for frictionally engaging the pair of frictional memberswith the first rotational member in a substantially direct manner or ina substantially indirect manner via a pair of frictional plates, whereinat least one of the frictional members is configured with pluralfrictional materials of approximately block-shape, the at least one ofthe frictional members is provided at the disc so that a frictionalsurface of the at least one of the frictional members is substantiallybetween 20 percent and 80 percent of an entire surface area of the discat which the at least one of the frictional members is provided.
 7. Atorque fluctuation absorbing device according to claim 6, wherein anarea between adjacent friction materials forming the at least one of thefrictional members penetrates from an inner peripheral side of the atleast one of the frictional members to an outer peripheral side of theat least one of the frictional members.
 8. A torque fluctuationabsorbing device according to claim 7, wherein the at least one of thepair of frictional members of approximately block-shape has anon-frictional portion at the frictional surface of the at least one ofthe pair of frictional members of approximately block-shape.
 9. A torquefluctuation absorbing device according to claim 8, wherein thenon-frictional portion at the frictional surface of the at least one ofthe pair of frictional members of approximately block-shape penetratesfrom the inner peripheral side of the at least one of the pair offrictional members to the outer peripheral side thereof.
 10. A torquefluctuation absorbing device according to claim 6, wherein the at leastone of the pair of frictional members of approximately block-shape has anon-frictional portion at the frictional surface of the at least one ofthe pair of frictional members.
 11. A torque fluctuation absorbingdevice according to claim 10, wherein the non-frictional portion at thefrictional surface of the at least one of the pair of frictional membersof approximately block-shape penetrates from an inner peripheral side ofthe at least one of the pair of frictional members to an outerperipheral side thereof.
 12. A torque fluctuation absorbing deviceaccording to claim 6, wherein the at least one of the pair of frictionalmembers is adhered at the disc.
 13. A torque fluctuation absorbingdevice according to claim 6, wherein the at least one of the pair offrictional members includes a projected portion, and the disc includes arecessed portion for fitting the projected portion therein.
 14. A torquefluctuation absorbing device according to claim 6, wherein the discincludes a hole for integrally connecting one of the pair of frictionalmembers fixed at a first surface of the disc with the other one of thepair of frictional members fixed at a second surface of the disc.
 15. Atorque fluctuation absorbing device according to claim 6, wherein atleast one of the pair of frictional members includes a reinforcingmember which is more rigid than the at least one of the pair offrictional members, and the reinforcing member projects at both radialend portions of the frictional surface less than at the vicinity of acentral portion of the frictional surface on the basis of a crosssectional view of the frictional member.